The present invention relates, in general, to the construction of spin vanes for directing gases through a passage and, in particular, to a new and useful low pressure drop vane for burners and NO.sub.x ports.
A key feature of burners and NO.sub.x ports used in industrial and utility boilers is the spin vanes in the secondary (or combustion) air zones. These spin vanes are used to change the flow direction of the incoming air to impart a swirl to the air as it exits the burner. The spin vanes are located in the annular flow passage(s) that surround the burner fuel nozzle or the core air flow passage in the NO.sub.x port. The spin vanes are fabricated from flat sheet material and are designed to be adjusted from a completely closed, to a fully open position in the annular flow passage.
Approximately one-half of the pressure drop across these burners and NO.sub.x ports is generated in the spin vane passage.
The pressure drop across the spin vanes becomes particularly important for low-NO.sub.x pulverized-coal burners if secondary air velocity has to increased from 4,500 to 6,500 feet per minute. The spin vane design needs to be improved to reduce pressure drop while maintaining swirl performance.
U.S. Pat. No. 5,257,927 discloses a low NO.sub.x burner using a central spin vane diffuser while U.S. Pat. No. 5,199,355 utilizes spin vane diffusers in concentric outer combustion passages. A compact flame holder combustor is also disclosed in U.S. Pat. No. 5,142,858. A boiler furnace register with vanes is disclosed in U.S. Pat. No. 4,927,352.
Various other patents disclose a variety of gas flow passages and registers, ports, burners, blowers and the like, which use various vane configurations. As with the patents mentioned above, the vanes are all solid and are characterized by causing a certain pressure drop in the gas flow. The additional patents are as follows:
______________________________________ U.S. Pat. Nos. U.S. Pat. Nos. ______________________________________ 5,302,115 3,720,495 5,207,008 3,356,122 5,145,361 3,349,826 5,112,220 3,299,841 5,101,633 3,198,235 5,092,762 3,179,152 4,681,532 3,049,085 4,519,322 2,782,738 4,504,217 2,747,657 4,500,282 2,676,649 4,479,775 2,669,296 4,160,640 2,414,459 4,106,890 2,380,463 3,904,349 1,910,893. ______________________________________
It would thus be advantageous if a construction or a technique could be found which takes advantage of vanes, in particular, spin vanes, in a gas flow passage, while reducing the pressure drop caused by such vanes.